1. Field of the Invention
The present invention relates to a process for preparing enaminocarbonyl compounds.
2. Description of Related Art
Particular substituted enaminocarbonyl compounds are known as insecticidally active compounds from EP 0 539 588 A1. In addition, international patent applications WO 2007/115644, WO 2007/115643 and WO 2007/115646 also describe corresponding insecticidally active enaminocarbonyl compounds.
In general, enaminocarbonyl compounds are synthesized from tetronic acid and an amine according to scheme 1 below. This procedure is described, for example, in EP 0 539 588 A1 and in Heterocycles vol. 27, 8, pages 1907 to 1923 (1988).

A particular disadvantage of this process is that anhydrous tetronic acid is required as a starting compound, the preparation of which is inconvenient and costly.
For instance, tetronic acid is generally prepared proceeding from ethyl acetoacetate via a bromination and subsequent hydrogenation (cf. Synthetic Communication, 11(5), pages 385 to 390 (1981)). The overall yield of tetronic acid proceeding from ethyl acetoacetate is less than 40%, which means that the process is not very attractive from an industrial point of view.
Swiss patent 503 722 describes a further process for preparing tetronic acid. This involves reacting ethyl 4-chloroacetoacetate with an aromatic amine to give 3-arylaminocrotonolactone, and then the tetronic acid is released by treatment with mineral acids. The disadvantage of this process is that the isolation of the tetronic acid is possible only by high-vacuum sublimation, which means that this process too is not very attractive from an industrial point of view.
A further process for preparing tetronic acid is described in EP 0 153 615 A, which proceeds from 2,4-dichloroacetoacetates. This likewise multistage and complicated process likewise affords the desired compound only with a moderate overall yield of 65%.
Tetrahedron Letters, 31, pages 2683 and 2684 (1974) describes the preparation of tetronic acid and of a corresponding enaminocarbonyl compound. The synthesis described there is reproduced in scheme 2 below. The reactant used is dimethyl acetylenedicarboxylate.

Disadvantages of this process are the low overall yield of only 30% and the requirement to use costly reactants, for example lithium aluminium hydride (LiAlH4) as reagents.
Additionally known from the prior art is a process for preparing enaminocarbonyl compounds proceeding from methyl tetronate (J. Heterocyclic Chem., 21, 1753 (1984)). For this process, the starting material used is the costly 4-bromo-3-methoxybut-3-enecarboxylic ester.
A further process proceeds from a 4-chloroacetoacetic ester, which is reacted with amines (Heterocycles, vol. 27, 8, 1988, pages 1907 to 1923). The reaction to give the aminofuran is performed in one step. This involves adding the amine with glacial acetic acid to a solution of ethyl 4-chloroacetoacetate in benzene, and heating the resulting mixture under reflux for several hours. The yields of 4-methylamino-2(5H)-furanone in this synthesis are only 40%.
EP 0 123 095 A discloses a process in which tetronamide is prepared from 3-amino-4-acetoxycrotonic ester. 3-Amino-4-acetoxycrotonic ester is costly and inconvenient to prepare, and so an economically viable synthesis is not possible by this process.
A further process for preparing tetronic acid proceeding from malonic esters and chloroacetyl chloride is known from J. Chem. Soc., Perkin Trans. 1 (1972), 9/10, pages 1225 to 1231. This process affords the desired target compound with a yield of only 43%.
WO 2007/115644 describes the preparation of enaminocarbonyl compounds, for example of 4-[[(6-chloropyridin-3-yl)methyl](3,3-dichloroprop-2-en-1-yl)amino]furan-2(5H)-one by reaction of 4-[[(6-chloropyridin-3-yl)methyl]amino]furan-2(5H)-one with 3-bromo-1,1-dichloroprop-1-ene (cf. Preparation Example, Method 2, Example (3)). WO 2007/115644 also describes the preparation of enaminocarbonyl compounds, for example of 4-[[(6-chloropyridin-3-yl)methyl](2-fluoroethyl)amino]furan-2(5H)-one by reaction of 4-[[(2-fluoroethyl)amino]furan-2(5H)-one with 2-chloro-5-chloromethylpyridine (cf. Preparation Examples, Method 3, Example (4)). The reactions are preferably performed with hydrides of lithium or sodium. The substrates are generally costly and at the same time can be handled only with difficulty for safety reasons.
In WO 2009/036899, which claims the priority of European patent application 07116639, enaminocarbonyl compounds are prepared, for example, proceeding from 4-(methoxycarbonyl)-5-oxo-2,5-dihydrofuran-3-ol and an amine.

where    R1 is hydrogen, alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, halocycloalkyl, alkoxy, alkyloxyalkyl, halocycloalkylalkyl or arylalkyl;    Z is hydrogen, alkali metal or alkaline earth metal; and    A is pyrid-2-yl or pyrid-4-yl, or is pyrid-3-yl which is optionally 6-substituted by fluorine, chlorine, bromine, methyl, trifluoromethyl or trifluoromethoxy, or is pyridazin-3-yl which is optionally 6-substituted by chlorine or methyl, or is pyrazin-3-yl or is 2-chloropyrazin-5-yl or is 1,3-thiazol-5-yl which is optionally 2-substituted by chlorine or methyl, or is pyrimidinyl, pyrazolyl, thiophenyl, oxazolyl, isoxazolyl, 1,2,4-oxadiazolyl, isothiazolyl, 1,2,4-triazolyl or 1,2,5-thiadiazolyl, which is optionally substituted by fluorine, chlorine, bromine, cyano, nitro, C1-C4-alkyl (which is optionally substituted by fluorine and/or chlorine), C1-C3-alkylthio (which is optionally substituted by fluorine and/or chlorine), or C1-C3-alkylsulphonyl (which is optionally substituted by fluorine and/or chlorine), or is
                where        X is halogen, alkyl or haloalkyl and        Y is halogen, alkyl, haloalkyl, haloalkoxy, azido or cyano.        